To improve the cooling efficiency of a transformer operated in a wind power station, there is provided a cooling system comprising a transformer guard housing having a first opening for supply of a transformer cooling medium and having a second opening for discharge of the transformer cooling medium. Further, a first channel system supplies the transformer cooling medium to the transformer guard housing. A second channel system discharges the transformer cooling medium from the transformer guard housing. Through the provision of the cooling system, a controlled flow of cooling medium to the transformer accommodated in the transformer guard housing increases operative efficiency of the installation.